1. Field of the Invention
The present invention relates to a communication service continuation system. In particular, the present invention relates to a communication service continuation system which enables to select and switch communication unit for using communication services corresponding to the situation, and also relates to a communication service continuation method and a program thereof.
2. Related Art
In information and telecommunication services, communication networks are constructed corresponding to the characteristics of terminals and service contents respectively, including fixed-line telephone networks for fixed-line telephones, mobile communication networks (W-CDMA, PDCP, GPRS, etc.) for mobile telephones, and data communication networks (IEEE802.11 for wireless LAN, ADSL, ISDN, etc.) for data communications performed by computers.
In recent years, as computers become smaller and have higher performance, various kinds of terminals are available. Further, as networks become broadband, audio and visual data having large amount of information can be transmitted through data communication networks such as IP.
With such changes in the information technology and the communication technology, boundaries between fixed telephone networks, mobile communication networks and data communication networks become blurred in their structures. Therefore, needs for terminals including various kinds of communication unit increase among general users, so that needs for communication services which can be used beyond the boundaries of communication networks also increase.
In a wireless communication system, a method of preventing loss of communication data at a time of handover in which base stations are switched has been well known generally, an example of which is disclosed in Japanese Patent Application Laid-Open No. 2003-153327 (Patent Document 1).
However, the art in Patent Document 1 is limited to performing handover in a mobile communication network, so it cannot be applied as a method for switching a communication network itself to be used.
In the example described above, in the case where communication unit and communication networks are switched while executing a communication service in a mobile terminal including a plurality of communication unit, the communication service being executed must be stopped for a while and a communicating connection must be established with another communication unit to be used. This causes a problem that communication unit cannot be switched while maintaining execution of the communication service.
Further, in the example described above, in the case where a communication unit is switched to another one while maintaining the executing state of the communication service utilizing a communicating connection with the communication unit, a problem that a loss or delay of communication data is unavoidable is caused.
Specifically, if a user of a mobile terminal using a communication service through a mobile telephone network becomes able to connect with a wireless LAN in an office for example on which larger capacity communication can be performed at higher speed, or if a user using a communication service through an optical fiber network on a LAN in the office wants to continuously use the communication service through a mobile telephone network outside the company, it has been practically impossible to switch communication unit while maintaining the execution of the communication service being used because a loss of data mentioned above cannot be avoidable.